Sociologists Dalton Conley of New York University and Emily Rauscher of the University of Kansas, who conducted the study, say that overall, "compared to those with no daughters, parents with all daughters are 14 percent less likely to identify as a Democrat" and are "11 percent more likely to identify as a Republican than parents with no daughters."

The sociologists also found that the daughters effect is far more significant among better-educated and wealthier parents, while the figures for the less-educated and lower-income earners are insignificant.

As for possible reasons for their findings, the researchers say parents with daughters could want more "socially conservative policies" and, therefore, are more likely to support the GOP.

Their results are based on information collected in 1994 from 661 respondents with biological children interviewed for the 1994 General Social Survey, conducted by the University of Chicago’s National Opinion Research Center.

This national survey has been conducted regularly since 1972, but the 1994 survey is the only one that included questions about the sex and birth order of a respondent’s biological children.

The new research is consistent with a Pew Research Council study in June that found boys who grew up with sisters in their household were more likely to grow up to be Republicans. Researchers Andrew Healy and Neil Malhotra said that "having sisters makes males more politically conservative in terms of their gender role attitudes and their partisanship."